     (+ (* years (per-year unit span))
        (quot units span))))
 
+;; The following partial functions take care of the issue with delta
+;; above, by calculating the span in periods across years.
+
 (def months (partial delta-periods month 1))
 (def sixteens (partial delta-periods julian 16))
 (def eights (partial delta-periods julian 8))
+
+;; We currently choose the period-func based on the resolution of the
+;; data. This will have to be amended, as some datasets at different
+;; temporal resolutions do indeed have the same spatial resolution.
 
 (def period-func
   {"1000" months

;; first of each month, while the others mark off blocks of 16 or 8
;; julian days from the beginning of the year.
;;
;;(It's important to note that time periods are NOT measured from the
;; activation date of a specific product. The first available NDVI
;; 16-day composite, for example, has a beginning date of February
;; 18th 2001, or Julian day 49, the 1st day of the 4th period as


;; In developing the time period conversion functions, we noticed that
;; as long as the time period remained consistent from dataset to
;; dataset, the ability to 0-index each dataset became irrelevant.
;; Our choice of January 1st, 2000 as a common reference date ensures
;; that, regardless of the date on which the specific MODIS product
;; became active, datasets at the same temporal resolution will match
;; up.

(def ref-date (date-time 2000))

